Portable coordinate measurement machine

ABSTRACT

A portable articulated arm coordinate measurement machine is provided. An articulated arm is provided having a plurality of arm segments. Each arm segment includes an angular encoder for producing a signal corresponding to an angle of rotation. A shaft rotates which about an axis is attached to an inner portion of a first and second bearing. A patterned disk is attached to the shaft. A housing is attached to an outer portion of the first and second bearing. A read head is attached to the housing in proximity to the patterned disk which produces an electrical signal in response to an angle of rotation. The patterned disk and the first arm segment supported for rotation about the axis by only the first and second bearing. A circuit receives the electrical signal and provides an angle and data corresponding to a position of the probe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/412,744filed on Mar. 6, 2012. The Ser. No. 13/412,744 application is acontinuation of application Ser. No. 13/412,705 filed on Mar. 6, 2012.The Ser. No. 13/412,705 application is a continuation of applicationSer. No. 13/017,751, filed on Jan. 31, 2011. The Ser. No. 13/017,751application is a continuation of application Ser. No. 12/178,994, filedon Jul. 24, 2008. The Ser. No. 12/178,994 application is acontinuation-in-part (CIP) of application Ser. No. 11/765,726, filed onJun. 20, 2007, now U.S. Pat. No. 7,519,493. The Ser. No. 11/765,726application is a continuation-in-part (CIP) of application Ser. No.11/334,091, filed on Jan. 18, 2006, now U.S. Pat. No. 7,246,030, whichin turn is a continuation-in-part (CIP) of application Ser. No.11/141,444, filed on May 31, 2005, now U.S. Pat. No. 7,050,930, which inturn is a continuation application of application Ser. No. 10/366,678,filed on Feb. 13, 2003, now U.S. Pat. No. 6,965,843, and claims thebenefit of Provisional Application Ser. Nos. 60/394,908, filed on Jul.10, 2002 and 60/357,599, filed on Feb. 14, 2002. The contents of all ofthe aforementioned applications are hereby incorporated into the presentContinuation application by reference, and domestic priority is claimedin the present Continuation application to all of the applicationslisted above.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to coordinate measurement machines(CMMs) and in particular to portable CMM's having a handle that includeselectronics.

2. Prior Art

Currently, portable articulated arms are provided as a measurementsystem with a host computer and applications software. The articulatedarm is commonly used to measure points on an object and these measuredpoints are compared to computer-aided design (CAD) data stored on thehost computer to determine if the object is within the CADspecification. In other words, the CAD data is the reference data towhich actual measurements made by the articulated arm are compared. Thehost computer may also contain applications software that guides theoperator through the inspection process. For many situations involvingcomplicated applications, this arrangement is appropriate since the userwill observe the three-dimensional CAD data on the host computer whileresponding to complex commands in the applications software.

An example of a prior art portable CMM for use in the above-discussedmeasurement system is disclosed in U.S. Pat. No. 5,402,582 ('582), whichis assigned to the assignee hereof and incorporated herein by reference.The '582 patent discloses a conventional three-dimensional measuringsystem composed of a manually operated multi-jointed articulated armhaving a support base on one end thereof and a measurement probe at theother end. Commonly assigned U.S. Pat. No. 5,611,147 ('147), which isagain incorporated herein by reference, discloses a similar CMM havingan articulated arm. In this patent, the articulated arm includes anumber of important features including an additional rotational axis atthe probe end thus providing for an arm with either a two-one-three or atwo-two-three joint configuration (the latter case being a 7 axis arm)as well as improved pre-loaded bearing constructions for the bearings inthe arm.

Commonly assigned U.S. Pat. No. 5,978,748 ('748), which is incorporatedherein by reference, discloses an articulated arm having an on-boardcontroller which stores one or more executable programs and whichprovides the user with instructions (e.g., inspection procedures) andstores the CAD data that serves as the reference data. In the '748patent, a controller is mounted to the arm and runs the executableprogram which directs the user through a process such as an inspectionprocedure. In such a system, a host computer may be used to generate theexecutable program.

The prior art devices are limited in that they are capable of measuringonly one point in space at a time. Products have become available thatreplace the single point probe with a line laser scanner andcharge-coupled device (CCD) that are capable of simultaneously measuringa locus of points on the surface of an object that lie on a planedefined by a scanning laser. An example of such a prior art product isthe ScanWorks™ manufactured by Perceptron of Plymouth, Mich. However,such prior art devices are retrofit onto the existing articulated armsof portable CMM's and require external, high bandwidth data connectionsfrom the scanner to the host computer used to interpret the image datagenerated by the CCD as well as external connections to power supplies.Thus, the electrical lines extend outside the housing of the articulatedarm. Furthermore, when the single-point probe is replaced by the linelaser scanner retrofit, the highly accurate single point probefunctionality is lost or at least diminished.

SUMMARY OF THE INVENTION

In accordance with an embodiment, a portable articulated arm coordinatemeasurement machine is provided. The coordinate measurement machineincluding a manually positionable articulated arm having opposed firstand second ends, the articulated arm including a plurality of connectedarm segments, the plurality of arm segments including a first armsegment, each arm segment including at least one angular encoder forproducing a signal corresponding to an angle of rotation, each angularencoder including a read head and a patterned disk, each patterned diskhaving a periodic pattern of a measurable characteristic. A base sectionis connected to the second end. A probe is connected to the first end. Ashaft is fixedly attached to an inner portion of a first bearing and aninner portion of a second bearing, the shaft configured to rotate aboutan axis passing substantially through a center of the first bearing anda center of the second bearing, the shaft configured to fixedly couplewith the first arm segment. A patterned disk is fixedly attached to theshaft. A housing is fixedly attached to an outer portion of the firstbearing and an outer portion of the second bearing. A read head isfixedly attached to the housing, the read head in proximity to thepatterned disk, the read head configured to produce a electrical signalin response to a angle of rotation about the axis of the shaft relativeto the housing, the patterned disk and the first arm segment supportedfor rotation about the axis by only the first bearing and the secondbearing. An electrical circuit is configured to receive the electricalsignal, to provide a angle based at least in part on the electricalsignal, and to provide data corresponding to a position of the probe,the data based at least in part on the angle.

In accordance with another embodiment, another portable articulated armcoordinate measurement machine is provided. The coordinate measurementmachine including a manually positionable articulated arm having opposedfirst and second ends, the articulated arm including a plurality ofconnected arm segments, the plurality of arm segments including a firstarm segment, each arm segment including at least one angular encoder forproducing a signal corresponding to an angle of rotation, each angularencoder including a read head and a patterned disk, each patterned diskhaving a periodic pattern of a measurable characteristic. A base sectionis connected to the second end. A probe is connected to the first end. Ashaft is fixedly attached to an inner portion of a first bearing and aninner portion of a second bearing, the shaft configured to rotate aboutan axis passing substantially through a center of the first bearing anda center of the second bearing, the shaft configured to fixedly couplewith the first arm segment. A read head is fixedly attached to theshaft. A housing is fixedly attached to an outer portion of the firstbearing and an outer portion of the second bearing. A patterned disk isfixedly attached to the housing, the patterned disk in proximity to theread head, the patterned disk configured to produce an electrical signalin response to an angle of rotation about the axis of the shaft relativeto the housing, the read head and the first arm segment supported forrotation about the axis by only the first bearing and the secondbearing. An electrical circuit is configured to receive the electricalsignal, to provide an angle based at least in part on the electricalsignal, and to provide data corresponding to a position of the probe,the data based at least in part on the angle.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein like elements are number alike inthe several FIGURES:

FIG. 1 is a front perspective view of the portable CMM of the presentinvention including an articulated arm and attached host computer;

FIG. 2 is a rear perspective view of the CMM of FIG. 1;

FIG. 3 is a right side view of the CMM of FIG. 1 (with the host computerremoved);

FIG. 3A is a right side view of the CMM of FIG. 1 with slightly modifiedprotective sleeves covering two of the long joints;

FIG. 4 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base and the first articulated armsection;

FIG. 5 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base, first arm section and partiallyexploded second arm section;

FIG. 6 is a partially exploded, perspective view of the CMM of thepresent invention depicting the base, first arm section, second armsection and partially exploded third arm section;

FIG. 7 is an exploded, perspective view depicting a pair ofencoder/bearing cartridges being assembled between two dual socketjoints in accordance with the present invention;

FIG. 8 is a front elevation view of the bearing/encoder cartridges anddual socket joints of FIG. 7;

FIG. 9 is an exploded, perspective view of a short bearing/encodercartridge in accordance with the present invention;

FIG. 9A is an exploded, perspective view similar to FIG. 9, but showinga single read head;

FIG. 9B is an exploded, perspective view, similar to FIG. 9, but showingfour read heads;

FIG. 9C is a perspective view of FIG. 9B after assembly;

FIG. 9D is an exploded, perspective view, similar to FIG. 9, but showingthree read heads;

FIG. 9E is a perspective view of FIG. 9D after assembly;

FIG. 10 is a cross-sectional elevation view of the cartridge of FIG. 9;

FIG. 11 is an exploded, perspective view of a long bearing/encodercartridge in accordance with the present invention;

FIG. 11A is an exploded, perspective view similar to FIG. 11, butshowing a single read head;

FIG. 12 is a cross-sectional elevation view of the cartridge of FIG. 11;

FIG. 12A is a cross-sectional elevation view of the cartridge of FIG. 12depicting the dual read heads being rotatable with the shaft;

FIG. 13 is an exploded, perspective view of still anotherbearing/encoder cartridge in accordance with the present invention;

FIG. 13A is an exploded, perspective view similar to FIG. 13, butshowing a single read head;

FIG. 14 is a cross-sectional elevation view of the cartridge of FIG. 13;

FIG. 15 is an exploded, perspective view of a bearing/encoder cartridgeand counter balance spring in accordance with the present invention;

FIG. 15A is an exploded, perspective view similar to FIG. 15, butshowing a single read head;

FIG. 16 is a cross-sectional elevation view of the cartridge and counterbalance of FIG. 15;

FIG. 17 is a top plan view of a dual read head assembly for a largerdiameter bearing/encoder cartridge used in accordance with the presentinvention;

FIG. 18 is a cross-sectional elevation view along the line 18-18 of FIG.17;

FIG. 19 is a bottom plan view of the dual read head assembly of FIG. 17;

FIG. 20 is a top plan view of a dual read head assembly for a smallerdiameter bearing/encoder cartridge in accordance with the presentinvention;

FIG. 21 is a cross-sectional elevation view along the line 21-21 of FIG.20;

FIG. 22 is a bottom plan view of the dual read head assembly of FIG. 20;

FIG. 23A is a block diagram depicting the electronics configuration forthe CMM of the present invention using a single read head and FIG. 23Bis a block diagram depicting the electronics configuration for the CMMof the present invention using a dual read head;

FIG. 24 is a cross-sectional elevation view longitudinally through theCMM of the present invention (with the base removed);

FIG. 24A is a cross-sectional elevation view of the CMM of FIG. 3A;

FIG. 25 is an enlarged cross-sectional view of a portion of FIG. 24depicting the base and first long joint segment of the CMM of FIG. 24;

FIG. 25A is a perspective view of the interconnection between a long andshort joint in accordance with an alternative embodiment of the presentinvention;

FIG. 25B is a cross-sectional elevation view longitudinally through aportion of FIG. 25A;

FIG. 26 is an enlarged cross-sectional view of a portion of FIG. 24depicting the second and third long joint segments;

FIGS. 26A and B are enlarged cross-sectional views of portions of FIG.24A depicting the second and third long joints as well as the probe;

FIG. 27 is a cross-sectional, side elevation view through a firstembodiment of the measurement probe in accordance with the presentinvention;

FIG. 27A is a side elevation view of another embodiment of a measurementprobe in accordance with the present invention;

FIG. 27B is a cross-sectional elevation view along the line 27B-27B ofFIG. 27A;

FIG. 27C is a perspective view of a pair of “take” or “confirm” switchesused in FIGS. 27A-B;

FIGS. 28A-C are sequential elevation plan views depicting the integratedtouch probe assembly and conversion to hard probe assembly in accordancewith the present invention;

FIG. 29 is a cross-sectional, side elevation view through still anotherembodiment of a measurement probe in accordance with the presentinvention;

FIG. 30 is a side elevation view of a measurement probe with a seventhaxis transducer;

FIG. 31 is a side elevation view, similar to FIG. 30, but including aremovable handle;

FIG. 32 is an end view of the measurement probe of FIG. 31;

FIG. 33 is a cross-sectional elevation view of the measurement probe ofFIG. 31;

FIG. 34A is a side-perspective view of a first embodiment of theintegrated line scanner of the present invention;

FIG. 34B is a partially cut-away, perspective view of the integratedline scanner of FIG. 34A;

FIG. 35 is a front perspective view of the portable CMM of the presentinvention including an articulated arm with integrated line laserscanner and attached host computer;

FIG. 36 is a side profile of the hand-held line laser scanner unitportion of the articulated arm of FIG. 35 schematically showingoperation thereof;

FIG. 37 is a top plan view of the hand held line laser scanner unit ofFIG. 36 showing operation thereof;

FIG. 38 is a cross-section view of the hand-held line laser scanner ofFIG. 36;

FIG. 39 is a block diagram depicting operation of the articulated arm ofFIG. 35 with integrated line laser scanner;

FIG. 40 is a perspective view of yet another embodiment of a line laserscanner mounted on the measurement probe of FIG. 31;

FIGS. 41 and 42 are respectively rear and front perspective views of theline laser scanner of FIG. 40;

FIGS. 43, 44 and 45 are respectively side-elevation, front, and rearviews of the line laser scanner of FIG. 40;

FIG. 46 is a front elevation view, similar to FIG. 44 of the line laserscanner of FIG. 40;

FIG. 47 is a cross-sectional elevation view along the line 47-47 of FIG.46;

FIG. 48 is a partially exploded view depicting the attachment of a linelaser scanner onto the probe of FIG. 31;

FIG. 49 is a front perspective view depicting a kinematic mount usedwith the line laser scanner of FIG. 40; and

FIG. 50 is a rear perspective view of the kinematic mount of FIG. 49.

FIG. 51 is a perspective view of an additional embodiment having athermally stabilized laser.

FIG. 52 is a side view of the thermally stabilized laser of FIG. 51.

FIG. 53 is a cross-sectional side view of the line laser scanner of FIG.51.

FIG. 54 is a front view of the line laser scanner of FIG. 51 taken alongsection A-A of FIG. 53.

FIG. 55 is a top view of the calibration plate.

FIG. 56 is side view of the line laser scanner moving about thecalibration plate.

FIG. 57 is side view of the line laser scanner rotated 90 degrees fromthe position FIG. 56 moving about the calibration plate.

FIG. 58 is side view of the line laser scanner moving about thecalibration plate.

FIG. 59 is a perspective view of a fiber coupled lased diode of anembodiment.

FIG. 60 is a perspective view a wireless laser scanner embodiment.

FIG. 61 is a perspective view a multiple laser scanner head embodiment.

FIG. 62 is a perspective view of a bracket with a temperature sensoraccording to at least an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIGS. 1-3, the CMM of the present invention is showngenerally at 10. CMM 10 comprises a multijointed, manually operated,articulated arm 14 attached at one end to a base section 12 and attachedat the other end to a measurement probe 28. Arm 14 is constructed ofbasically two types of joints, namely a long joint (for swivel motion)and a short joint (for hinge motion). The long joints are positionedsubstantially axially or longitudinally along the arm while the shortjoints are preferably positioned at 90° to the longitudinal axis of thearm. The long and short joints are paired up in what is commonly knownas a 2-2-2 configuration (although other joint configurations such as2-1-2, 2-1-3, 2-2-3, etc. may be employed) Each of these joint pairs areshown in FIGS. 4-6.

FIG. 4 depicts an exploded view of the first joint pair, namely longjoint 16 and short joint 18. FIG. 4 also depicts an exploded view of thebase 12 including a portable power supply electronics 20, a portablebattery pack 22, a magnetic mount 24 and a two-piece base housing 26Aand 26B. All of these components will be discussed in more detailhereinafter.

Significantly, it will be appreciated that the diameters of the variousprimary components of articulated arm 14 will taper from the base 12 tothe probe 28. Such taper may be continuous or, as in the embodimentshown in the FIGURES, the taper may be discontinuous or step-wise. Inaddition, each of the primary components of articulated arm 14 may bethreadably attached thereby eliminating a large number of fastenersassociated with prior art CMMs. For example, and as will be discussedhereafter, magnetic mount 24 is threadably attached to first long joint16. Preferably, such threading is tapered threading which isself-locking and provides for increased axial/bending stiffness.Alternatively, as shown in FIGS. 25A and 25B, and as discussedhereafter, the primary components of the articulated arm may havecomplimentary tapered male and female ends with associated flanges, suchflanges being bolted together.

Referring to FIG. 5, the second set of a long and short joint is shownbeing attached to the first set. The second joint set includes longjoint 30 and short joint 32. As is consistent with the attachment ofmagnetic mount 24 to long joint 16, long joint 30 is threadably attachedto threading on the interior surface of long joint 16. Similarly, andwith reference to FIG. 6, the third joint set includes a third longjoint 34 and a third short joint 36. Third long joint 34 threadablyattaches to threading on the interior surface of second short joint 32.As will be discussed in more detail hereinafter, probe 28 threadablyattaches to short joint 36.

Preferably, each short joint 18, 32 and 36 is constructed of cast and/ormachined aluminum components or alternatively, lightweight stiff alloyor composite. Each long joint 16, 30 and 34 is preferably constructed ofcast and/or machined aluminum, lightweight stiff alloy and/or fiberreinforced polymer. The mechanical axes of the three aforementionedjoint pairs (i.e., pair 1 comprises joint pairs 16, 18, pair 2 comprisesjoint pairs 30, 32 and pair 3 comprises joint pairs 34, 36) are alignedwith respect to the base for smooth, uniform mechanical behavior. Theaforementioned tapered construction from base 12 to probe 28 ispreferred to promote increased stiffness at the base where loads aregreater and smaller profile at the probe or handle where unobstructeduse is important. As will be discussed in more detail hereinafter, eachshort joint is associated with a protective bumper 38 on either endthereof and each long probe is covered with a protective sleeve 40 or41. It will be appreciated that the first long joint 16 is protected bythe base housing 26A, B which provides the same type of protection assleeves 40, 41 provide for the second and third long joints 30, 34.

In accordance with an important feature of the present invention, eachof the joints of the articulated arm utilizes a modular bearing/encodercartridge such as the short cartridge 42 and the long cartridge 44 shownin FIGS. 7 and 8. These cartridges 42, 44 are mounted in the openings ofdual socket joints 46, 48. Each socket joint 46, 48 includes a firstcylindrical extension 47 having a first recess or socket 120 and asecond cylindrical extension 49 having a second recess or socket 51.Generally, sockets 120 and 51 are positioned 90 degrees to one anotheralthough other relative, angular configurations may be employed. Shortcartridge 42 is positioned in each socket 51 of dual socket joints 46and 48 to define a hinge joint, while long cartridge 44 is positioned insocket 120 of joint 46 (see FIG. 25) and long cartridge 44′ (see FIG.26) is positioned in socket 120 of joint 48 to each define alongitudinal swivel joint. Modular bearing/encoder cartridges 42, 44permit the separate manufacture of a pre-stressed or preloaded dualbearing cartridge on which is mounted the modular encoder components.This bearing encoder cartridge can then be fixedly attached to theexternal skeletal components (i.e., the dual socket joints 46, 48) ofthe articulated arm 14. The use of such cartridges is a significantadvance in the field as it permits high quality, high speed productionof these sophisticated subcomponents of articulated arm 14.

In the embodiment described herein, there are four different cartridgetypes, two long axial cartridges for joints 30 and 34, one base axialcartridge for joint 16, one base cartridge (which includes a counterbalance) for short joint 18 and two hinge cartridges for joints 32 and36. In addition, as is consistent with the taper of articulated arm 14,the cartridges nearest the base (e.g., located in long joint 16 andshort joint 18) have a larger diameter relative to the smaller diametersof joints 30, 32, 34 and 36. Each cartridge includes a pre-loadedbearing arrangement and a transducer which in this embodiment comprisesa digital encoder. Turning to FIGS. 9 and 10, the cartridge 44positioned in axial long joint 16 will now be described.

Cartridge 44 includes a pair of bearings 50, 52 separated by an innersleeve 54 and outer sleeve 56. It is important that bearings 50, 52 arepre-loaded. In this embodiment, such preload is provided by sleeves 54,56 being of differing lengths (inner sleeve 54 is shorter than outersleeve 56 by approximately 0.0005 inch) so that upon tightening, apreselected preload is generated on bearings 50, 52. Bearings 50, 52 aresealed using seals 58 with this assembly being rotatably mounted onshaft 60. At its upper surface, shaft 60 terminates at a shaft upperhousing 62. An annulus 63 is defined between shaft 60 and shaft upperhousing 62. This entire assembly is positioned within outer cartridgehousing 64 with the shaft and its bearing assembly being securelyattached to housing 64 using a combination of an inner nut 66 and anouter nut 68. Note that upon assembly, the upper portion 65 of outerhousing 64 will be received within annulus 63. It will be appreciatedthat the aforementioned preload is provided to bearings 50, 52 upon thetightening of the inner and outer nuts 66, 68 which provide compressionforces to the bearings and, because of the difference in length betweenthe inner and outer spacers 54, 56, the desired preload will be applied.

Preferably, bearings 50, 52 are duplex ball bearings. In order to obtainthe adequate pre-loading, it is important that the bearing faces be asparallel as possible. The parallelism affects the evenness of thepre-loading about the circumference of the bearing. Uneven loading willgive the bearing a rough uneven running torque feel and will result inunpredictable radial run out and reduced encoder performance. Radial runout of the modularly mounted encoder disk (to be discussed below) willresult in an undesirable fringe pattern shift beneath the reader head.This results in significant encoder angular measurement errors.Furthermore, the stiffness of the preferably duplex bearing structure isdirectly related to the separation of the bearings. The farther apartthe bearings, the stiffer will be the assembly. The spacers 54, 56 areused to enhance the separation of the bearings. Since the cartridgehousing 64 is preferably aluminum, then the spacers 54, 56 will alsopreferably be made from aluminum and precision machined in length andparallelism. As a result, changes in temperature will not result indifferential expansion which would compromise the preload. As mentioned,the preload is established by designing in a known difference in thelength of spacers 54, 56. Once the nuts 66, 68 are fully tightened, thisdifferential in length will result in a bearing preload. The use ofseals 58 provide sealed bearings since any contamination thereof wouldeffect all rotational movement and encoder accuracy, as well as jointfeel.

While cartridge 44 preferably includes a pair of spaced bearings,cartridge 44 could alternatively include a single bearing or three ormore bearings. Thus, each cartridge needs at least one bearing as aminimum.

The joint cartridges of the present invention may either have unlimitedrotation or as an alternative, may have a limited rotation. For alimited rotation, a groove 70 on a flange 72 on the outer surface ofhousing 64 provides a cylindrical track which receives a shuttle 74.Shuttle 74 will ride within track 70 until it abuts a removable shuttlestop such as the rotation stop set screws 76 whereupon rotation will beprecluded. The amount of rotation can vary depending on what is desired.In a preferred embodiment, shuttle rotation would be limited to lessthan 720°. Rotational shuttle stops of the type herein are described inmore detail in commonly owned U.S. Pat. No. 5,611,147, all of thecontents of which have been incorporated herein by reference.

As mentioned, in an alternative embodiment, the joint used in thepresent invention may have unlimited rotation. In this latter case, aknown slip ring assembly is used. Preferably, shaft 60 has a hollow oraxial opening 78 therethrough which has a larger diameter section 80 atone end thereof. Abutting the shoulder defined at the intersectionbetween axial openings 78 and 80 is a cylindrical slip ring assembly 82.Slip ring assembly 82 is non-structural (that is, provides no mechanicalfunction but only provides an electrical and/or signal transferfunction) with respect to the preloaded bearing assembly set forth inthe modular joint cartridge. While slip ring assembly 82 may consist ofany commercially available slip ring, in a preferred embodiment, slipring assembly 82 comprises an H series slip ring available from IDMElectronics Ltd. of Reading, Berkshire, United Kingdom. Such slip ringsare compact in size and with their cylindrical design, are ideallysuited for use in the opening 80 within shaft 60. Axial opening 80through shaft 60 terminates at an aperture 84 which communicates with achannel 86 sized and configured to receive wiring from the slip ringassembly 82. Such wiring is secured in place and protected by a wirecover 88 which snaps onto and is received into channel 86 and aperture84. Such wiring is shown diagrammatically at 90 in FIG. 10.

As mentioned, modular cartridge 44 include both a preloaded bearingstructure which has been described above as well as a modular encoderstructure which will now be described. Still referring to FIGS. 9 and10, the preferred transducer used in the present invention comprises amodular optical encoder having two primary components, a read head 92and a grating disk 94. In this embodiment, a pair of read heads 92 arepositioned on a read head connector board 96. Connector board 96 isattached (via fasteners 98) to a mounting plate 100. Disk 94 ispreferably attached to the lower bearing surface 102 of shaft 60(preferably using a suitable adhesive) and will be spaced from and inalignment with read heads 92 (which is supported and held by plate 100).A wire funnel 104 and sealing cap 106 provide the final outer coveringto the lower end of housing 64. Wire funnel 104 will capture and retainwiring 90 as best shown in FIG. 10. It will be appreciated that theencoder disk 94 will be retained by and rotate with shaft 60 due to theapplication of adhesive at 102. FIGS. 9 and 10 depict a double read head92; however, it will be appreciated that more than two read heads may beused or, in the alternative, a single read head as shown in FIG. 9A maybe used. FIGS. 9B-E depict examples of modular cartridges 44 with morethan two read heads. FIGS. 9B-C show four read heads 92 received in aplate 100 and spaced at 90 degree intervals (although different relativespacings may be appropriate). FIGS. 9D-E show three read heads 92received in a plate 100 and spaced at 120 degree intervals (althoughdifferent relative spacing may be appropriate).

In order to properly align disk 94, a hole (not shown) is providedthrough housing 64 at a location adjacent disk 94. A tool (not shown) isthen used to push disk 94 into proper alignment whereupon adhesivebetween disk 94 and shaft 66 is cured to lock disk 94 in place. A holeplug 73 is then provided through the hole in housing 64.

It is important to note that the locations of disk 94 and read head 92may be reversed whereby disk 94 is attached to housing 56 and read head92 rotates with shaft 60. Such an embodiment is shown in FIG. 12A whereboard 96′ is attached (via adhesive) to shaft 60′ for rotationtherewith. A pair of read heads 92′ are attached to board 96′ and thuswill rotate with shaft 60′. The disk 94′ is positioned on a support 100′which is attached to housing 64′. In any event, it will be appreciatedthat either the disk 94 or read head 92 may be mounted for rotation withthe shaft. All that is important is that disk 94 and read head 92 bepositioned in a cartridge (or joint) so as to be rotatable with respectto each other while maintaining optical communication.

Preferably, the rotational encoder employed in the present invention issimilar to that disclosed in U.S. Pat. Nos. 5,486,923 and 5,559,600, allof the contents of which are incorporated herein by reference. Suchmodular encoders are commercially available from MicroE Systems underthe trade name Pure Precision Optics. These encoders are based onphysical optics that detect the interference between diffraction ordersto produce nearly perfect sinusoidal signals from a photo detector array(e.g., read head(s)) inserted in the fringe pattern. The sinusoidalsignals are electronically interpolated to allow detection ofdisplacement that is only a fraction of the optical fringe.

Using a laser light source, the laser beam is first collimated by a lensand then sized by an aperture. The collimated size beam passes through agrating that diffracts the light into discrete orders with the 0^(th)and all even orders suppressed by the grating construction. With the 0order suppressed, a region exists beyond the diverging 3^(rd) orderwhere only the ±1^(st) orders overlap to create a nearly pure sinusoidalinterference. One or more photodetector arrays (read heads) are placedwithin this region, and produces four channels of nearly pure sinusoidaloutput when there is relative motion between the grating and thedetector. Electronics amplify, normalize and interpolate the output tothe desired level of resolution.

The simplicity of this encoder design yields several advantages overprior art optical encoders. Measurements may be made with only a lasersource and its collimating optics, a diffractive grating, and a detectorarray. This results in an extremely compact encoder system relative tothe bulkier prior art, conventional encoders. In addition, a directrelationship between the grating and the fringe movement desensitizesthe encoder from environmentally induced errors to which prior artdevices are susceptible. Furthermore, because the region of interferenceis large, and because nearly sinusoidal interference is obtainedeverywhere within this region, alignment tolerances are far more relaxedthan is associated with prior art encoders.

A significant advantage of the aforementioned optical encoder is thatthe precision of the standoff orientation and distance or the distanceand orientation of the read head with respect to the encoder disk is farless stringent. This permits a high accuracy rotational measurement andan easy-to-assemble package. The result of using this “geometrytolerant” encoder technology results in a CMM 10 having significant costreductions and ease of manufacturing.

It will be appreciated that while the preferred embodiment describedabove includes an optical disk 94, the preferred embodiment of thepresent invention also encompasses any optical fringe pattern whichallow the read head to measure relative motion. As used herein, suchfringe pattern means any periodic array of optical elements whichprovide for the measurement of motion. Such optical elements or fringepattern could be mounted on a rotating or stationary disk as describedabove, or alternatively, could be deposited, secured or otherwisepositioned or reside upon any of the relatively moving components (suchas the shaft, bearings or housing) of the cartridge.

Indeed, the read head and associated periodic array or pattern does notnecessarily need to be based on optics (as described above) at all.Rather, in a broader sense, the read head could read (or sense) someother periodic pattern of some other measurable quantity orcharacteristic which can be used to measure motion, generally rotarymotion. Such other measurable characteristics may include, for example,reflectivity, opacity, magnetic field, capacitance, inductance orsurface roughness. (Note that a surface roughness pattern could be readusing a read head or sensor in the form of a camera such as a CCDcamera). In such cases, the read head would measure, for example,periodic changes in magnetic field, reflectivity, capacitance,inductance, surface roughness or the like. As used herein therefore, theterm “read head” means any sensor or transducer and associatedelectronics for analysis of these measurable quantities orcharacteristics with an optical read head being just one preferredexample. Of course, the periodic pattern being read by the read head canreside on any surface so long as there is relative (generally rotary)motion between the read head and periodic pattern. Examples of theperiodic pattern include a magnetic, inductive or capacitive mediadeposited on a rotary or stationary component in a pattern. Moreover, ifsurface roughness is the periodic pattern to be read, there is no needto deposit or otherwise provide a separate periodic media since thesurface roughness of any component in communication with the associatedread head (probably a camera such as a CCD camera) may be used.

As mentioned, FIGS. 9 and 10 depict the elements of the modular bearingand encoder cartridge for axially long joint 16. FIGS. 11 and 12 depictthe bearing and encoder cartridge for axial long joints 30 and 34. Thesecartridge assemblies are substantially similar to that shown FIGS. 9 and10 and so are designated by 44′. Minor differences are evident from theFIGURES relative to cartridge 44 with respect to, for example, adifferently configured wire cap/cover 88′, slightly differing wirefunnels/covers 104′, 106′ and the positioning of flange 72′ at the upperend of housing 64′. Also, the flanges between housing 64′ and shaftupper housing 62 are flared outwardly. Of course, the relative lengthsof the various components shown in FIGS. 11 and 12 may differ slightlyfrom that shown in FIGS. 9 and 10. Since all of these components aresubstantially similar, the components have been given the sameidentification numeral with the addition of a prime. FIG. 11A is similarto FIG. 11, but depicts a single read head embodiment.

Turning to FIGS. 13 and 14, similar exploded and cross-sectional viewsare shown for the bearing and encoder cartridges in short hinge joints32 and 36. As in the long axial joints 44′ of FIGS. 11 and 12, thecartridges for the short hinge joints 32 and 36 are substantiallysimilar to the cartridge 44 discussed in detail above and therefore thecomponents of these cartridges are identified at 44″ with similarcomponents being identified using a double prime. It will be appreciatedthat because cartridges 44″ are intended for use in short joints 32, 36,no slip ring assembly is required as the wiring will simply pass throughthe axial openings 78″, 80″ due to the hinged motion of these joints.FIG. 13A is similar to FIG. 13, but depicts a single read headembodiment.

Finally, with reference to FIGS. 15 and 16, the modular bearing/encodercartridge for short hinge joint 18 is shown at 108. It will beappreciated that substantially all of the components of cartridge 108are similar or the same as the components in cartridges 44, 44′ and 44″with the important exception being the inclusion of a counter balanceassembly. This counter balance assembly includes a counter balancespring 110 which is received over housing 64″ and provides an importantcounter balance function to CMM 10. FIG. 15A is similar to FIG. 15, butdepicts a single read head embodiment.

As mentioned, in a preferred embodiment, more than one read head may beused in the encoder. It will be appreciated that angle measurement of anencoder is effected by disk run out or radial motion due to appliedloads. It has been determined that two read heads positioned at 180°from each other will result in run out causing cancellation effects ineach read head. These cancellation effects are averaged for a final“immune” angle measurement. Thus, the use of two read heads and theresultant error cancellation will result in a less error prone and moreaccurate encoder measurement. FIGS. 17-19 depict the bottom,cross-sectional and top views respectively for a dual read headembodiment useful in, for example, a larger diameter cartridge such asfound in joints 16 and 18 (that is, those joints nearest the base).Thus, a cartridge end cap 100 has mounted thereto a pair of circuitboards 96 with each circuit board 96 having a read head 92 mechanicallyattached thereto. The read heads 92 are preferably positioned 180° apartfrom each other to provide for the error cancellation resulting from therun out or radial motion of the disk. Each board 96 additionallyincludes a connector 93 for attachment of the circuit board 96 to theinternal bus and/or other wiring as will be discussed hereinafter. FIGS.20-22 depict substantially the same components as in FIGS. 17-19 withthe primary difference being a smaller diameter cartridge end cap 100.This smaller diameter dual read head embodiment would be associated withthe smaller diameter cartridges of, for example, joints 30, 32, 34 and36.

Turning now to FIG. 23A, a block diagram of the electronics is shown forthe single read head embodiment of FIGS. 9A, 11A, 13A and 15A. It willbe appreciated that CMM 10 preferably includes an external bus(preferably a USB bus) 260 and an internal bus (preferably RS-485) 261which is designed to be expandable for more encoders as well as eitheran externally mounted rail or additional rotational axes such as aseventh axis. The internal bus is preferably consistent with RS485 andthis bus is preferably configured to be used as a serial network in amanner consistent with the serial network for communicating data fromtransducers in a portable CMM arm as disclosed in commonly assigned U.S.Pat. No. 6,219,928, all of the contents of which have been incorporatedherein by reference.

With reference to FIG. 23A, it will be appreciated that each encoder ineach cartridge is associated with an encoder board. The encoder boardfor the cartridge in joint 16 is positioned within base 12 and isidentified at 112 in FIG. 25. The encoders for joints 18 and 30 areprocessed on a dual encoder board which is located in the second longjoint 30 and is identified at 114 in FIG. 26. FIG. 26 also depicts asimilar dual encoder board 116 for the encoders used in joints 32 and34, board 116 being positioned in third long joint 34 as shown in FIG.26. Finally, the end encoder board 118 is positioned within measurementprobe handle 28 as shown in FIG. 24 and is used to process the encodersin short joint 36. Each of the boards 114, 116 and 118 are associatedwith a thermocouple to provide for thermal compensation due totemperature transients. Each board 112, 114, 116 and 118 incorporatesembedded analog-to-digital conversion, encoder counting and serial portcommunications. Each board also has read programmable flash memory toallow local storage of operating data. The main processor board 112 isalso field programmable through the external USB bus 260. As mentioned,the internal bus (RS-485) 261 is designed to be expandable for moreencoders which also includes either an externally mounted rail and/orseventh rotation axis. An axis port has been provided to provideinternal bus diagnosis. Multiple CMMs of the type depicted at 10 inthese FIGURES may be attached to a single application due to thecapabilities of the external USB communications protocol. Moreover,multiple applications may be attached to a single CMM 10 for the verysame reasons.

Preferably, each board 112, 114, 116 and 118 includes a 16-bit digitalsignal processor such as the processor available from Motorola under thedesignation DSP56F807. This single processing component combines manyprocessing features including serial communication, quadrature decoding,A/D converters and on-board memory thus allowing a reduction of thetotal number of chips needed for each board.

In accordance with another important feature of the present invention,each of the encoders is associated with an individualized identificationchip 121. This chip will identify each individual encoder and thereforewill identify each individual bearing/encoder modular cartridge so as toease and expedite quality control, testing, and repair.

FIG. 23B is an electronics block diagram which is similar to FIG. 23A,but depicts the dual read head embodiment of FIGS. 10, 12, 14 and 16-22.

With reference to FIGS. 24-26, the assembly of each cartridge in thearticulated arm 14 will now be described (note that FIG. 24 depicts arm10 without base 12. Note also that FIGS. 24-26 employ the single readhead embodiments of FIGS. 9A, 11A, 13A and 15A). As shown in FIG. 25,the first long joint 16 includes a relatively long cartridge 44, theupper end of which has been inserted into a cylindrical socket 120 ofdual socket joint 46. Cartridge 44 is securely retained within socket120 using a suitable adhesive. The opposite, lower end of cartridge 44is inserted into an extension tube, which in this embodiment may be analuminum sleeve 122 (but sleeve 122 may also be comprised of a stiffalloy or composite material). Cartridge 44 is secured in sleeve 122again using a suitable adhesive. The lower end of sleeve 122 includes alarger outer diameter section 124 having internal threading 126 thereon.Such threading is outwardly tapered and is configured to threadably matewith inwardly tapered threading 128 on magnetic mount housing 130 as isclearly shown in FIG. 4. As has been discussed, all of the severaljoints of CMM 10 are interconnected using such tapered threading.Preferably, the tapered thread is of the NPT type which isself-tightening and therefore no lock nuts or other fastening devicesare needed. This threading also allows for and should include a threadlocking agent.

Turning to FIG. 26, as in first long joint 16, long cartridge 44′ isadhesively secured in the cylindrical opening 120′ of dual socket joint46′. The outer housing 64′ of cartridge 44′ includes a shoulder 132defined by the lower surface of flange 72′. This shoulder 132 supportscylindrical extension tube 134 which is provided over and surrounds theouter surface of housing 64′. Extension tubes are used in the joints tocreate a variable length tube for attachment to a threaded component.Extension tube 134 thus extends outwardly from the bottom of cartridge64′ and has inserted therein a threaded sleeve 136. Appropriate adhesiveis used to bond housing 44′ to extension tube 134 as well as to bondsleeve 136 and tube 134 together. Sleeve 136 terminates at a taperedsection having outer threading 138 thereon. Outer threading threadablymates with internal threading 140 on connecting piece 142 which has beenadhesively secured in opening 144 of dual socket joint 48. Preferably,extension tube 134 is composed of a composite material such as anappropriate carbon fiber composite while threadable sleeve 136 iscomposed of aluminum so as to match the thermal properties of the dualsocket joint 48. It will be appreciated that PC board 114 is fastened toa support 146 which in turn is secured to dual socket joint support 142.

In addition to the aforementioned threaded connections, one, some or allof the joints may be interconnected using threaded fasteners as shown inFIGS. 25A-B. Rather than the threaded sleeve 136 of FIG. 26, sleeve 136′of FIG. 25B has a smooth tapered end 137 which is received in acomplimentary tapered socket support 142′. A flange 139 extendscircumferentially outwardly from sleeve 136′ with an array of bolt holes(in this case 6) therethrough for receiving threaded bolts 141. Bolts141 are threadably received in corresponding holes along the uppersurface of socket support 142′. An extension tube 134′ is received oversleeve 136′ as in the FIG. 26 embodiment. The complimentary tapered maleand female interconnections for the joints provide improved connectioninterfaces relative to the prior art.

Still referring to FIG. 26, long cartridge 44″ of third long joint 34 issecured to arm 14 in a manner similar to cartridge 44′ of long joint 30.That is, the upper portion of cartridge 44″ is adhesively secured intoan opening 120″ of dual socket joint 46″. An extension tube 148(preferably composed of a composite material as described with respectto tube 134) is positioned over outer housing 64″ and extends outwardlythereof so as to receive a mating sleeve 150 which is adhesively securedto the interior diameter of extension tube 148. Mating sleeve 150terminates at a tapered section having outer threading 152 and mateswith complimentary interior threading 153 on dual socket joint support154 which has been adhesively attached to a cylindrical socket 156within dual socket joint 148′. Printed circuit board 116 is similarlyconnected to the dual socket joint using the PCB support 146′ which issecured to dual socket joint support 154.

As discussed with respect to FIGS. 7 and 8, the short cartridges 44′ inFIGS. 13 and 14 and 108 of FIG. 15 are simply positioned between twodual socket joints 46, 48 and are secured within the dual socket jointsusing an appropriate adhesive. As a result, the long and shortcartridges are easily attached to each other at right angles (or, ifdesired, at angles other than right angles).

The modular bearing/transducer cartridges as described above constitutean important technological advance in portable CMM's such as shown, forexample, in U.S. Pat. No. 5,794,356 to Raab and U.S. Pat. No. 5,829,148to Eaton. This is because the cartridge (or housing of the cartridge)actually defines a structural element of each joint which makes up thearticulated arm. As used herein, “structural element” means that thesurface of the cartridge (e.g., the cartridge housing) is rigidlyattached to the other structural components of the articulated arm inorder to transfer rotation without deformation of the arm (or at most,with only de minimis deformation). This is in contrast to conventionalportable CMM's (such as disclosed in the Raab '356 and Eaton '148patents) wherein separate and distinct joint elements and transferelements are required with the rotary encoders being part of the jointelements (but not the transfer elements). In essence, the presentinvention has eliminated the need for separate transfer elements (e.g.,transfer members) by combining the functionality of the joint andtransfer elements into a singular modular component (i.e., cartridge).Hence, rather than an articulated arm comprised of separate and distinctjoints and transfer members, the present invention utilizes anarticulated arm made up of a combination of longer and shorter jointelements (i.e., cartridges), all of which are structural elements of thearm. This leads to better efficiencies relative to the prior art. Forexample, the number of bearings used in a joint/transfer membercombination in the '148 and '582 patent was four (two bearings in thejoint and two bearings in the transfer member) whereas the modularbearing/transducer cartridge of the present invention may utilize aminimum of one bearing (although two bearings are preferred) and stillaccomplish the same functionality (although in a different and improvedway).

FIGS. 24A and 26A-B are cross-sectional views, similar to FIGS. 24-26,but showing the dual read head embodiments of FIGS. 10, 12, 14 and 16-22and are further cross-sections of the CMM 10′ shown in FIG. 3A.

The overall length of articulated arm 14 and/or the various arm segmentsmay vary depending on its intended application. In one embodiment, thearticulated arm may have an overall length of about 24 inches andprovide measurements on the order of about 0.0002 inch to 0.0005 inch.This arm dimension and measurement accuracy provides a portable CMMwhich is well suited for measurements now accomplished using typicalhand tools such as micrometers, height gages, calipers and the like. Ofcourse, articulated arm 14 could have smaller or larger dimensions andaccuracy levels. For example, larger arms may have an overall length of8 or 12 feet and associated measurement accuracies of 0.001 inch thusallowing for use in most real time inspection applications or for use inreverse engineering.

CMM 10 may also be used with a controller mounted thereto and used torun a relatively simplified executable program as disclosed inaforementioned U.S. Pat. No. 5,978,748 and application Ser. No.09/775,226; or may be used with more complex programs on host computer172.

With reference to FIGS. 1-6 and 24-26, in a preferred embodiment, eachof the long and short joints are protected by an elastomeric bumper orcover which acts to limit high impact shock and provide ergonomicallypleasant gripping locations (as well as an aesthetically pleasingappearance). The long joints 16, 30 and 34 are all protected by a rigidplastic (e.g., ABS) replaceable cover which serves as an impact andabrasion protector. For the first long joint 16, this rigid plasticreplaceable cover comes in the form of the two-piece base housing 26Aand 26B as is also shown in FIG. 4. Long joints 30 and 34 are eachprotected by a pair of cover pieces 40 and 41 which, as shown in FIGS. 5and 6 may be fastened together in a clam shell fashion using appropriatescrews so as to form a protective sleeve. It will be appreciated that ina preferred embodiment, this rigid plastic replaceable cover for eachlong joint 30 and 34 will surround the preferably composite (carbonfiber) extension tube 134 and 148, respectively.

Preferably, one of the covers, in this case cover section 41, includes aslanted support post 166 integrally molded therein which limits therotation at the elbow of the arm so as to restrict probe 28 fromcolliding with base 12 in the rest position. This is best shown in FIGS.3, 24 and 26. It will be appreciated that post 166 will thus limitunnecessary impact and abrasion.

As will be discussed with respect to FIGS. 29 and 31, probe 28 may alsoinclude a replaceable plastic protective cover made from a rigid plasticmaterial.

FIGS. 3A, 24A and 26A-B depict alternative protective sleeves 40′, 41′which also have a clam shell construction, but are held in place usingstraps or spring clips 167 rather than threaded fasteners.

Each of the short joints 18, 32 and 36 include a pair of elastomeric(e.g., thermoplastic rubber such as Santoprene®) bumpers 38 aspreviously mentioned and as shown clearly in FIGS. 1-3 and 5-6. Bumpers38 may either be attached using a threaded fastener, a suitable adhesiveor in any other suitable manner. Elastomeric or rubber bumper 38 willlimit the high impact shock as well as provide an aesthetically pleasingand ergonomically pleasant gripping location.

The foregoing covers 40, 41, 40′, 41′ and bumpers 38 are all easilyreplaceable (as is the base housing 26A, 26B) and allow arm 14 toquickly and inexpensively be refurbished without influencing themechanical performance of CMM 10.

Still referring to FIGS. 1-3, base-housing 26A, B includes at least twocylindrical bosses for the mounting of a sphere as shown at 168 in FIG.3. The sphere may be used for the mounting of a clamp type computerholder 170 which in turn supports a portable or other computer device172 (e.g., the “host computer”). Preferably, a cylindrical boss isprovided on either side of base housing 26A, B so that the ball andclamp computer mount may be mounted on either side of CMM 10.

Turning now to FIGS. 27 and 28 A-C, a preferred embodiment of themeasurement probe 28 will now be described. Probe 28 includes a housing196 having an interior space 198 therein for housing printed circuitboard 118. It will be appreciated that housing 196 constitutes a dualsocket joint of the type described above and includes a socket 197 inwhich is bonded a support member 199 for supporting circuit board 118.Preferably, handle 28 includes two switches, namely a take switch 200and a confirm switch 202. These switches are used by the operator toboth take a measurement (take switch 200) and to confirm the measurement(confirm switch 202) during operation. In accordance with an importantfeature of this invention, the switches are differentiated from eachother so as to minimize confusion during use. This differentiation maycome in one or more forms including, for example, the switches 200, 202being of differing height and/or differing textures (note that switch202 has an indentation as opposed to the smooth upper surface of switch200) and/or different colors (for example, switch 200 may be green andswitch 202 may be red). Also in accordance with an important feature ofthis invention, an indicator light 204 is associated with switches 200,202 for indicating proper probing. Preferably, the indicator light 204is a two-color light so that, for example, light 204 is green upontaking of a measurement (and pressing the green take button 200) and isred for confirming a measurement (and pressing the red button 202). Theuse of a muticolored light is easily accomplished using a known LED asthe light source for light 204. To assist in gripping, to provideimproved aesthetics and for impact resistance, an outer protectingcovering of the type described above is identified at 206 and providedover a portion of probe 28. A switch circuit board 208 is provided forthe mounting of buttons 200, 202 and lamp 204 and is supported bysupport member 199. Switch board 208 is electrically interconnected withboard 118 which houses components for processing the switches and lightindicator as well as for the processing of short hinge joint 36.

In accordance with another important feature of the present invention,and with reference to both FIG. 27 as well as FIGS. 28A-C, probe 28includes a permanently installed touch trigger probe as well as aremovable cap for adapting a fixed probe while protecting the touchtrigger probe. The touch probe mechanism is shown at 210 in FIG. 27 andis based on a simplified three point kinematics seat. This conventionalconstruction comprises a nose 212 which contacts a ball 214 biased by acontact spring 216. Three contact pins (one pin being shown at 218) arein contact with an underlying electric circuit. Application of anyforces against the probe nose 212 results in lifting of any one of thethree contact pins 218 resulting in an opening of the underlyingelectric circuit and hence activation of a switch. Preferably, touchtrigger probe 210 will operate in conjunction with the front “take”switch 200.

As shown in FIG. 28B, when using touch trigger probe 210, a protectivethreaded cover 220 is threadably attached to threading 222 surroundingtrigger probe 210. However, when it is desired to use a fixed proberather than the touch trigger probe, the removable cap 220 is removedand a desired fixed probe such as that shown at 224 in FIGS. 27 and28A-C is threadably attached to threading 222. It will be appreciatedthat while fixed probe 224 has a round ball 226 attached thereto, anydifferent and desired fixed probe configuration may be easily threadablyattached to probe 28 via threading 222. Touch trigger probe assembly 210is mounted in a housing 228 which is threadably received into threadedconnector 230 which forms a part of probe housing 196. This threadableinterconnection provides for the full integration of touch trigger probe210 into probe 28. The provision of a fully integrated touch proberepresents an important feature of the present invention and isdistinguishable from prior art detachable touch probes associated withprior art CMMs. In addition, the permanently installed touch triggerprobe is also easily convertible to a hard probe as described above.

FIGS. 27A-C disclose yet another preferred embodiment for a measurementprobe in accordance with the present invention. In FIGS. 27A-C, ameasurement probe is shown at 28′ and is substantially similar tomeasurement probe 28 in FIG. 27 with the primary difference residing inthe configuration of the “take” and “confirm” switches. Rather than thediscrete button type switches shown in FIG. 27, measurement probe 28′utilizes two pairs of arcuate oblong switches 200 a-b and 202 a-b. Eachrespective pair of oblong switches 202 a-b and 200 a-b correspondrespectively to the take switch and the confirm switch as describedabove with respect to FIG. 27. An advantage of the measurement probe 28′embodiment relative to the measurement probe 28 embodiment is that eachpair of oblong switches 202 and 200 surround virtually the entirecircumference (or at least the majority of the circumference) of themeasurement probe and therefore are more easily actuatable by theoperator of the portable CMM. As in the FIG. 27 embodiment, an indicatorlight 204 is associated with each switch with the light 204 and switches200, 202 being mounted on respective circuit boards 208′. Also, as inthe FIG. 27 embodiment, switches 200, 202 may be differentiated usingfor example, different heights, different textures and/or differentcolors. Preferably, switches 200, 202 have a slight float such that thebutton may be actuated when pressed down in any location therealong. Asin the FIG. 27 embodiment, an outer protective covering of the typedescribed above is used at 206 and provided over a portion of probe 28′.

Referring now to FIG. 29, an alternative measurement probe for use withCMM 10 is shown generally at 232. Measurement probe 232 is similar tomeasurement probe 28 of FIG. 27 with the primary difference being thatprobe 232 includes a rotating handle cover 234. Rotating cover 234 ismounted on a pair of spaced bearings 236, 238 which in turn are mountedon an inner core or support 240 such that cover 234 is freely rotatable(via bearings 236, 238) about inner core 240. Bearings 236, 238 arepreferably radial bearings and minimize the parasitic torques on the armdue to probe handling. Significantly, the switch plate 208′ andcorresponding switches 200′, 202′ and LED 204′ are all mounted torotating handle cover 234 for rotation therewith. During rotation,electrical connectivity to processing circuit board 118′ is providedusing a conventional slip ring mechanism 242 which comprises a knownplurality of spaced spring fingers 242 which contact stationary circularchannels 244. In turn, these contact channels 244 are electricallyconnected to circuit board 118′. The rotating handle cover 234 andswitch assembly is thus electrically coupled to the inner core or probeshaft 240 and electronics board 118′ using the slip ring conductor 242.The rotation of the probe handle 234 permits switches 200′, 202′ to beoriented conveniently for the user. This allows the articulated arm 14′to measure accurately during handling by minimizing undocumented forces.The cover 234 is preferably comprised of a rigid polymer and is providedwith appropriate indentations 246 and 248 to allow easy and convenientgripping and manipulation by the probe operator.

It will be appreciated that the remainder of probe 232 is quite similarto probe 28 including the provision of a permanently and integrallyinstalled touch probe 210 in cover 220. Note that switches 200′, 202′are of differing heights and surface textures so as to provide ease ofidentification.

The rotating cover 234 is a significant advance in the CMM field in thatit can alleviate the need for an additional (i.e., seventh) axis ofrotation at the probe such as disclosed in aforementioned U.S. Pat. No.5,611,147. It will be appreciated that the addition of a seventh axisleads to a more complex and expensive CMM as well as the addition ofpossible error into the system. The use of the rotatable probe 232alleviates the need for a “true” seventh axis as it permits the probe toprovide the rotation needed for handle position at the probe end withoutthe complexity of a seventh transducer and associated bearings, encoderand electronics.

In the event that it is desired to utilize a measurement probe having a“true” seventh axis, that is, having a measurement probe with a seventhrotary encoder for measuring rotary rotation, such a measurement probeis shown in FIGS. 30-33. With reference to such FIGURES, a measurementprobe 500 is shown with such measurement probe being substantiallysimilar to the measurement probe in FIG. 27 with the primary differencebeing the insertion of a modular bearing/transducer cartridge 502 of thetype described above, the presence of the take and confirm switches 504,506 on the sides of the measurement probe and the inclusion of aremovable handle 508.

It will be appreciated that the modular bearing/transducer cartridge 502is substantially similar to the cartridges described in detail above andinclude a rotatable shaft, a pair of bearings on the shaft, an opticalencoder disk, at least one and preferably two optical read heads spacedfrom and in optical communication with the encoder disk and a housingsurrounding the bearings, optical encoder disk, read head(s) and atleast a portion of the shaft so as to define the discrete modularbearing/transducer cartridge. A circuit board 503 for the encoderelectronics resides in an opening 505 with probe 500. Pairs of take andconfirm buttons 504, 506 are positioned on either side of a downwardlyprojected housing portion 510 of probe 500 with the buttons beingconnected to an appropriate PC board 512 as in the measurement probe ofthe FIG. 27 embodiment. Similarly, an indicator light 513 is positionedbetween buttons 504, 506 as in the previously discussed embodiments. Apair of threaded openings 514 in housing 510 receive fasteners forremovable attachment of handle 508 which provides for ease of rotarymanipulation during use of measurement probe 500.

In all other substantial respects, measurement probe 500 is similar tomeasurement probe 28 of FIG. 27 including the preferred use ofpermanently installed touch trigger probe at 516 as well as a removablecap for adapting a fixed probe 518 while protecting the touch triggerprobe. It will be appreciated that the seventh rotary encoder 502included in measurement probe 500 facilitates the use of CMM 10 inconnection with known line laser scanners and other peripheral devices.

Turning now to FIGS. 2-4, 23 and 25, in accordance with an importantfeature of the present invention, a portable power supply is provided topower CMM 10 thus providing a fully portable CMM. This is in contrast toprior art CMMs where power supply was based only on an AC cord. Inaddition, CMM 10 may also be powered directly by an AC cord through anAC/DC adapter via a conventional plug-in socket. As shown in FIGS. 2, 3and 25, a conventional rechargeable battery (e.g., Li-ion battery) isshown at 22. Battery 22 is mechanically and electrically connected intoa conventional battery support 252 which in turn is electricallyconnected to a conventional power supply and battery recharger circuitcomponent 254 located on circuit board 20. Also communicating with board20 is an on/off switch 258 (see FIG. 3) and a high-speed communicationport 260 (preferably a USB port). The joint electronics of arm 14 isconnected to board 20 using an RS-485 bus. Battery 22 can be charged ona separate charger, or charged in place in cradle 252 as is commonlyfound in conventional video cameras. It will be appreciated thatportable computer 172 (see FIG. 2) can operate for several hours on itsbuilt-in batteries and/or in the alternative, may be electricallyconnected to the power supply unit 254 of CMM 10.

The on-board power supply/recharger unit in accordance with the presentinvention is preferably positioned as an integral part of CMM 10 bylocating this component as an integral part of base 12 and morespecifically as a part of the plastic base housing 26A, B. Note alsothat preferably, base housing 26A, B includes a small storage area 259having a pivotable lid 262 for storing spare batteries, probes, or thelike.

Turning now to FIGS. 34A and 34B, a line laser scanner 312 is shownwhich has been fully integrated onto probe 28, 28,′ 232, or morepreferably, probe 500. Line laser scanner 312 includes a housing 314 forhousing a digital camera 316, a line laser 318 and the appropriateelectronic circuitry 320. Housing 314 surrounds the probe 28 andincludes a handle 322 extending downwardly therefrom. Handle 322 iseasily accessible by the operator during use of the laser scanner. It isimportant that the laser scanner be rotatable so as to ensure correct,on-line measurements. To that end, housing 312 is mounted on anadditional (i.e., seventh) axis of rotation using an appropriate bearingstructure 324. In the preferred embodiment, this additional axis ofrotation includes a transducer and thus constitutes a totally separatejoint in addition to the typically five or six joints in the articulatedarm 14. More preferably, the additional axis is part of a three-axiswrist for the arm (leading to the typical 2-1-3 or 2-2-3 armconfiguration).

Preferably, the integrated touch probe and hard probe cover attachmentas described in FIGS. 27 and 28A-C are also employed in the embodimentof FIGS. 34A-B. The integrated line laser scanner 312 will operate in aknown and conventional fashion but unlike prior art devices which mustbe retrofitted onto the end of a portable CMM, the present invention isfully integrated onto the CMM. Thus, electronic circuitry 320 will befully integrated to the power and signal bus in articulated arm 14. As aresult, the laser scanner and CMM probe will be located in the samehousing, utilize the same internal wiring and constitute a unifiedmechanical structure. This structure will also permit the simultaneoususe or access of the laser scanner and the touch probe or hard probe.Moreover, circuitry 320 in cooperation with host computer 172 willprovide on-board image analysis and processing in real time and in aneasy to operate environment with signals from the laser scanner beingtransmitted via the RS-485 (or similar) serial communications bus.

Another embodiment of an integrated line laser scanner is shown in FIGS.35-39 where CMM 10 is shown with integrated line laser scanner/probe 600attached to probe 28. As shown in FIGS. 36 and 37, spaced back fromprobe 28 is a laser emitter window through which a scanning laser beam604 is emitted from scanning laser 601. Scanning laser 604 scans acrossa plane that lies perpendicular to the page as show in FIG. 36 andparallel to the page as shown in FIG. 37, which shows a plan view ofscanner/probe 600. Below laser emitter window 602 is CCD window 606. CCDwindow 606 may be in fact a focusing lens of a CCD 605 located withinhousing 610 as will be described in further detail below. CCD 605 has afield of view (FOV) as shown by dashed lines 608. The FOV of the CCD 605intersects the plane defined by scanning laser beam 604 within the area612 shown by dashed lines in FIG. 37. As will therefore be appreciated,when an object is passed through area 612, the locus of pointsintersecting area 612 on the object that face towards scanner/probe 600will be illuminated by scanning laser beam 604 and imaged by CCD 605.

The locus of points of an object illuminated by scanning laser beam 604will appear as a contour image on CCD 605. Since the location andorientation of line laser scanner/probe 600 is known by CMM 10, theprecise position of area 612 on the plane defined by scanning laser beam604 is known. As a point on an object that is illuminated by the beam ismoved closer or farther away from line laser scanner/probe 600, an imageof light reflected by the laser is moved up or down on the CCD imagingplane (not shown), while points to the left and right on the imagingplane of CCD 605 correspond to locations to the left and right of anobject intersecting area 612 and illuminated by scanning laser beam 604.Thus, each pixel of CCD 605 is associated with a corresponding locationin area 612 that is potentially illuminated by scanning laser beam 604and within the FOV of CCD 605.

Referring to FIGS. 38 and 39, image data from CCD 605 is processed onimage processing board 620, which is a circuit board within handle 611of housing 610. CCD 605 includes a sensor board for capturing imagesdetected by CCD 605 and converting them into a digital format, such asthe FIREWIRE data format established by Apple Computers, Inc. (or anysuitable high speed data communications protocol). The complete image isrelayed in real time to novel image processing board 620. Imageprocessing board 620 includes FIREWIRE interface 622, digital signalprocessor (DSP) 624, and memory 626. As the DSP receives image data, itprocesses it in real time. Software algorithms process each frame todetermine the precise location of the measured object with sub-pixelaccuracy. This is possible because the profile across the line laserapproximates a Gaussian function, and extends across multiple rows ofpixels on the CCD image plane. Selecting the appropriate pixel torepresent the line location is an important function of the software.The software algorithm analyzes the line profile along a pixel columnand calculates the “center of gravity” (COV), which can be a fractionalpixel location and is the point that best represents the exact locationof the line.

The algorithm proceeds to calculate the COV for each column in theframe. Once the frame is processed, the original image is discarded andonly the processed data is kept. The retained information is sent viacommunication chip 627 to the board at the base of the CMM in a mannersimilar to other data generated by the various digital encoders found ateach joint. The data packet generated by image processing board 620 is afraction of the size of the original image size and does not require asignificant amount of communication bandwidth. From the main CMMprocessor, the data is sent to the host CPU along with the coincidentarm position. The novel image processing board thus allows for on-boardimage processing within the arm 10 as opposed to the prior art wheresuch image processing is accomplished in a separate unit or computerhardwired to the laser scanner via an external retrofit.

As in previously discussed embodiments, handle 611 includes twoswitches, namely a take switch 200 and a confirm switch 202. Theseswitches are used by the operator in a probing mode to both take ameasurement (take switch 200) and to confirm the measurement (confirmswitch 202) during operation. Also, an indicator light 204 is associatedwith switches 200, 202 for indicating proper probing. Preferably, theindicator light 204 is a two-color light so that, for example, light 204is green upon taking of a measurement (and pressing the green takebutton 200) and is red for confirming a measurement (and pressing thered button 202). The use of a muticolored light is easily accomplishedusing a known LED as the light source for light 204.

In a scanning mode, take switch 200 activates the scanning processdescribed above while the confirm switch 202 may be used for some otherpurpose, e.g., to cancel the previous scan. In either mode, the functionof the switches may be assigned by the software program.

Probe 28 in FIG. 38 includes touch probe mechanism 210 and hard probecover 220 as previously described in FIGS. 27 and 30. Touch probemechanism 210 comprises a nose 212 which contacts a spring biasedelement. Three contact pins are in contact with an underlying electriccircuit. Application of force against the probe nose 212 results inlifting of one of the three contact pins resulting in an opening of theunderlying electric circuit and hence activation of a switch.Preferably, touch trigger probe 210 will operate in conjunction with thefront “take” switch 200 in a probe mode.

When using touch probe mechanism 210, a probe cover 220 is threadablyremoved. However, when it is desired to use a fixed probe rather thanthe touch trigger probe, probe cover 220 is attached as shown. It willbe appreciated that while probe cover 220 has a round ball 226 attachedthereto, any different and desired fixed probe configuration may beeasily threadably attached to probe 28. Touch probe mechanism 210 ismounted in a housing 228 which is threadably received into a threadedconnector which forms a part of probe housing 110.

Referring now to FIGS. 40-48, yet another embodiment of the line laserscanner is depicted at 700. In FIG. 40, laser scanner 700 is shownattached to a CMM 702 having the probe 500 of the type described inFIGS. 30-32. Turning to FIG. 47, laser scanner 700 includes a housing704 for housing the CCD window 606, focusing lens, image processingboard 620, high speed data communications protocol interface board 622,digital signal processor 624 and memory 626, all of which have beendescribed above in connection with the FIG. 38 embodiment.

Extending outwardly and downwardly from housing 704 is a kinematic ringwhich is best shown in FIGS. 49 and 50, and which includes three spaced(preferably, equidistantly or at 180 degrees apart) cut-outs or openings707. Each opening 707 receives a small cylindrical rod 708 therein.Cylindrical rods 708 are received in correspondingly spaced andcomplimentary shaped openings 710 on an inner face 712 of downwardlyprojected housing portion 510 of probe 500. A retaining ring 714 hasinternal threading 716 which is threadably received by threading 222 ofprobe 500 which then connects housing 704 tightly to probe 500 in aprecise alignment (resulting from the kinematic seat 706).

While laser scanner 700 operates in a similar manner to laser scanner600 of FIG. 38, scanner 700 has the advantage of being easily removablyattachable to the additional axis probe 500 (as opposed to the morepermanently attached laser scanners of FIGS. 24A and 38). Like thepreviously described laser scanner embodiments, the line laser scannerof FIGS. 40-48 provides a fully integrated scanning device comprised ofthe line laser, optical filters and digital camera, all of which areconnected to a high-speed data communications protocol (i.e., FIREWIRE)to a digital image processor, a DSP processor and memory for imageanalysis and three dimensional analysis and finally to a communicationsprocessor for communication of the resulting data packet to the bus ofthe articulated arm of CMM 10 and ultimately to the host computer 172.Significantly, the laser scanner 700 will utilize the power supply whichis already integrated into the arm of CMM 10. The only external cablenecessary in this embodiment is a short cable from the scanner housing704 to a connector on probe 500. This cable carries the power and signalbus connection for transmitting the data packet. Communication with thehost CPU 172 is integrated within the articulated arm so that noexternal communications cable is required as in the prior art devices.Thus, the laser scanner of this invention allows the internal digitalimaging processor board 620 to analyze imaging sensor data in real timewith the results of such an analysis being communicated back to the hostCPU with the coincident encoder position data. As discussed above, theprior art requires an external video processing unit and power supplywhich included cumbersome, bulky external cables.

In accordance with another feature of scanner 700, it is important thatthere be a rigid thermal and stable orientation between laser 602 andcamera 605, as well as a thermally stable connection between the housing704 and the additional axis probe 500. To that end, in accordance with apreferred embodiment, the internal construction of the frame 718 withinhousing 704 is made of a low coefficient of thermal expansion (CTE)material (for example, a mean CTE of between 1.0×10⁻⁶ to 10×10⁻⁶ in/in/°F.) which is preferably a metal alloy such as a steel/nickel alloy, forexample Invar (preferably Invar 36). This metal frame 718 extends beyondthe usually plastic housing 704 in the form of attachment ring 706 andallows the direct connection to the three point kinematic mountdescribed above. As mentioned, the three point kinematic mount 710 ispositioned at the base of the probe mount of the arm for receipt ofscanner housing 704. In addition, it will be appreciated that thekinematic mount 710 may also receive any other externally mounted sensoras necessary.

The laser scanner of FIGS. 34-48 may not only be used with the CMMsdescribed herein, but may be used with any other portable CMM havingarticulated arms such as described in the aforementioned U.S. Pat. Nos.5,796,356 or 5,829,148 or those articulated CMM arms manufactured byKosaka, Cimcore, Romer or others.

Turning to an additional embodiment, as shown in FIGS. 51-52, severaladditional features may be incorporated in comparison to the embodimentshown in FIG. 47. Elements which correspond to the elements shown inFIG. 47 have the identical reference numerals indicated herein in FIG.51-52. The corresponding elements have been respectfully described abovein connection with the embodiment of FIG. 47; however, the additionalelements described below may be used with any of the above embodiments.

As shown in FIG. 51, laser scanner 800 includes a housing 804. Unlikethe embodiment shown in FIG. 47 however, housing 804 does not includethe CCD window 806, which may comprise a clear window for example,because in this embodiment, CCD window 806 is mounted directly to thelens assembly 807. This eliminates any potential for movement betweenCCD window 806 and lens assembly 807.

Additionally as shown in FIGS. 51 and 53, a beam attenuator 808 has beenadded after the laser emitter window 802 to reduce the width of thescanning laser beam 604. The laser emitter window 802 may also bemounted directly to the scanning laser 801 or associated parts of thescanning laser 801 to reduce movement between the laser emitter window802 and the scanning laser 801.

Also, as shown in FIG. 52, the scanning laser 801 is thermallystabilized in this embodiment and may include at least one temperaturesensor 810 mounted to the scanning laser 801 for example and a heaterassembly 820 for example, which with control electronics (not shown),control and stabilize the temperature of the scanning laser 801. Athermally insulated sleeve 818 may also be located proximate to thescanning laser 801 as shown in FIG. 52 for example.

Plane Calibration

Additionally, any of the embodiments described above may include auseful and time saving plane calibration method as software or hardwarefor example which also reduces manufacturing costs. As described below,the method calibrates the embodiment CMM by use of the both the ballprobe 226 and the laser line scanner 800 using a single plane ofreference. For example, 6 degrees of freedom of the position of the linelaser scanner 800 may be found with respect to the last short joint 38of the arm nearest the probe 226 may be found using a single plane ofreference.

As shown in FIG. 55, to calibrate the CMM, a calibration plate 900 willbe digitized, first using the ball probe 226, and then second using thelaser line scanner 800.

Using the all probe 226, the white area 901 of the Calibration Plate 900will be digitized with the ball probe 226 touching the white surfacewith the ball probe and digitizing eight points 902 on the white area901 surface. Next, the ball probe is moved away from the white area 901.The flatness of the white area 901 surface is calculated and the resultsare displayed in a dialog box (not shown).

Next, as shown in FIG. 56, the white area 901 of the calibration plate900 is digitized using with the laser line scanner 800 also known as theLaser Line Probe (LLP). First, the laser is aimed at the middle of thewhite area 901 surface. The laser line scanner 800 is moved until thelaser is pointed in the center range by moving the laser line scanner800 to the center of the white area surface 901 in relation to the eightpoints 902.

Next as shown in FIG. 57, the laser line scanner 800 is rotated 90° andthe process above is repeated.

Next as shown in FIG. 58, the laser line scanner 800 is aimed at themiddle of the white surface 901 as above. However, the laser linescanner 800 is moved towards the white surface 901 until the laser is inthe Near Range 903, i.e., close to the surface of the white area 901.Then the laser line scanner 800 is moved to the Far Range 904 whilepointing to the center of the white surface.

The calibration points are then calculated and the probe CalibrationStatus is updated. If the probe passes, then the current date and timeis added to the probe information.

DRO

An embodiment software package may add a Digital ReadOut (DRO) Window tothe screen. The DRO window displays the current location of the probe inthe current coordinate system.

If the Laser Line Probe (LLP) is in range, the X, Y, Z coordinate is thecenter of the laser line. Note that this may not be the center of thecomplete laser line because some part of the laser line may be out ofrange.

Another embodiment is shown on FIG. 59. This embodiment eliminates thethermally stabilized scanning laser 801 apparatus shown in FIG. 52 andreplaces it with a fiber-coupled laser diode 801 a and line generator801 b. The laser diode 801 a is coupled to the fiber 801 c, and then thefiber is attached to a collimator 801 d and line generator 801 b. Theentire arrangement shown in FIG. 59 may be compacted tightly togetherand located in and substituted for the laser scanner 800 in the spaceoccupied by the thermally stabilized scanning laser 801 apparatus shownin FIG. 52 or may be placed in any desired arrangement.

A first advantage is this embodiment in comparison to a standard laserdiode arrangement, i.e., a laser diode without a fiber attached to it,is that use of the fiber launch method improves beam pointing stability,especially over varying temperature ranges. Another advantage of thefiber-coupled laser is that it reduces speckle. A third advantage ofthis embodiment, which does not require a heater (in comparison to analternative method of using a heater to control temperature) is thatelevated temperature from a heater may reduce life of the laser diode,increase use of power overall, and increase weight overall.

Another embodiment is shown in FIG. 60. This embodiment incorporateswireless data transfer technology to reduce or eliminate wiring and/ordata buses miming from the laser scanner 800 throughout the CMM 10 toany device such as controller computer 172 as shown in FIG. 1, or to anyother devices. An advantage of wireless technology is that data transferrates may be higher than a bus data transfer rate and/or use of thewireless transfer may free up the bus for other data. Other advantagesinclude the points that any reduction or elimination of wires reducesthe complexity of the rotating joints and the internals of the CMM 10while also reducing overall weight of the CMM 10 which is important forportability and ease of operation. Thus, wireless antenna 800 w withbuilt-in communications electronics is incorporated and communicateswith any desired wireless device such as an external host computer 172 aor any devices located within or on the CMM that have wirelesscapability according to any desired protocols. Thus, wireless datatransfer and communication capability for the CMM 10 is enabled andenvisioned for both transmission and reception of signals. Also,wireless data transfer can be adapted or retrofitted to any of theembodiments of this application and thus any wiring therein can be leftunused if a retrofit is implemented.

For example, in other embodiments described above, wires run through theCMM 10 and there are processors located inside the CMM 10. By using awireless system, the bus rate can be greatly reduced because the laserline scanner data at ˜20 kHz could be sent over the wireless channelinstead of over a bus. To provide one non-limiting example, the datarate for the CMM 10 could be increased to about 100 Hz from about 30 Hzin one example.

Another embodiment is shown in FIG. 61. In this embodiment, multiplelaser scanners 801 t 1 and 801 t 2 are located on a single arm of CMM10: The advantage of this is to cover more area in the same time. Acomparison of this embodiment to the single laser scanner embodimentshown in FIG. 48 for example readily illustrates the differences.

Another method and arrangement of holding the laser using steel pinsand/or set screws in a removable kinematic arrangement is disclosedherein. Benefits are cost and service related. Currently a method usinggluing items to a plate reduces serviceability and results in longerproduction times (while glue is drying). For example, the arrangementshown FIG. 38 may be modified so that scanning laser 601 may be held inplace by a removable mount comprised of steel pins and/or set screws inany suitable orientation.

As shown in FIG. 60, use of AlSi in the bracket 800 br and/or otherparts is also envisioned. The advantage of AlSi is that it is very stiffbut has a low density. The advantage of using this material for abracket is that the bracket can be made as stiff as possible withoutexceeding the allowable weight limit. Cartridges (42,44) or other partsmay also be made of AlSi. Benefits are reduced weight, increasedstiffness, and CTE close to steel allowing matching to bearings andbetter preloading.

FIG. 62 illustrates an embodiment that utilizes a temperature sensor 850mounted on bracket 840. In the embodiment of FIG. 62, there is nothermally insulated sleeve surrounding the laser 801. Thus, thetemperature of the bracket 840 is not stable and the bracket 840 maygrow or shrink with temperature changes. For example, error due tothermal expansion or contraction of the bracket may be approximately 16μm over 5 degrees Celsius. This example of expansion is not meant to belimiting in any way, but merely provided as one possible example.

Temperature sensor 850 can be used to compensate for thermal expansionor contraction of bracket 840. For example, pixel values reported by aCCD mounted on bracket 840 can be adjusted based on the readings of thetemperature sensor 850.

It will be understood that in conventional devices, this relativelysmall error due to thermal expansion of the bracket was not the primarycontributor to measurement errors. In other words, there weresignificant limits on accuracy that were larger than the contributionfrom thermal expansion of the bracket. Thus, it was not necessary tocompensate for thermal expansion of the bracket in conventional devices.However, as devices have become more accurate, it is helpful tocompensate for smaller or subtler sources of error, such as thermalexpansion of the bracket, in order to further improve the accuracy ofthe device.

One of ordinary skill in the art can appreciate that a computer or otherclient or server device can be deployed as part of a computer network,or in a distributed computing environment. In this regard, the methodsand apparatus described above and/or claimed herein pertain to anycomputer system having any number of memory or storage units, and anynumber of applications and processes occurring across any number ofstorage units or volumes, which may be used in connection with themethods and apparatus described above and/or claimed herein. Thus, thesame may apply to an environment with server computers and clientcomputers deployed in a network environment or distributed computingenvironment, having remote or local storage. The methods and apparatusdescribed above and/or claimed herein may also be applied to standalonecomputing devices, having programming language functionality,interpretation and execution capabilities for generating, receiving andtransmitting information in connection with remote or local services.

The methods and apparatus described above and/or claimed herein isoperational with numerous other general purpose or special purposecomputing system environments or configurations. Examples of well knowncomputing systems, environments, and/or configurations that may besuitable for use with the methods and apparatus described above and/orclaimed herein include, but are not limited to, personal computers,server computers, hand-held or laptop devices, multiprocessor systems,microprocessor-based systems, network PCs, minicomputers, mainframecomputers, distributed computing environments that include any of theabove systems or devices.

The methods described above and/or claimed herein may be described inthe general context of computer-executable instructions, such as programmodules, being executed by a computer. Program modules typically includeroutines, programs, objects, components, data structures, etc. thatperform particular tasks or implement particular abstract data types.Thus, the methods and apparatus described above and/or claimed hereinmay also be practiced in distributed computing environments such asbetween different power plants or different power generator units wheretasks are performed by remote processing devices that are linked througha communications network or other data transmission medium. In a typicaldistributed computing environment, program modules and routines or datamay be located in both local and remote computer storage media includingmemory storage devices. Distributed computing facilitates sharing ofcomputer resources and services by direct exchange between computingdevices and systems. These resources and services may include theexchange of information, cache storage, and disk storage for files.Distributed computing takes advantage of network connectivity, allowingclients to leverage their collective power to benefit the entireenterprise. In this regard, a variety of devices may have applications,objects or resources that may utilize the methods and apparatusdescribed above and/or claimed herein.

Computer programs implementing the method described above will commonlybe distributed to users on a distribution medium such as a CD-ROM. Theprogram could be copied to a hard disk or a similar intermediate storagemedium. When the programs are to be run, they will be loaded either fromtheir distribution medium or their intermediate storage medium into theexecution memory of the computer, thus configuring a computer to act inaccordance with the methods and apparatus described above.

The term “computer-readable medium” encompasses all distribution andstorage media, memory of a computer, and any other medium or devicecapable of storing for reading by a computer a computer programimplementing the method described above.

Thus, the various techniques described herein may be implemented inconnection with hardware or software or, where appropriate, with acombination of both. Thus, the methods and apparatus described aboveand/or claimed herein, or certain aspects or portions thereof, may takethe form of program code or instructions embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, or any othermachine-readable storage medium, wherein, when the program code isloaded into and executed by a machine, such as a computer, the machinebecomes an apparatus for practicing the methods and apparatus ofdescribed above and/or claimed herein. In the case of program codeexecution on programmable computers, the computing device will generallyinclude a processor, a storage medium readable by the processor, whichmay include volatile and non-volatile memory and/or storage elements, atleast one input device, and at least one output device. One or moreprograms that may utilize the techniques of the methods and apparatusdescribed above and/or claimed herein, e.g., through the use of a dataprocessing, may be implemented in a high level procedural or objectoriented programming language to communicate with a computer system.However, the program(s) can be implemented in assembly or machinelanguage, if desired. In any case, the language may be a compiled orinterpreted language, and combined with hardware implementations.

The methods and apparatus of described above and/or claimed herein mayalso be practiced via communications embodied in the form of programcode that is transmitted over some transmission medium, such as overelectrical wiring or cabling, through fiber optics, or via any otherform of transmission, wherein, when the program code is received andloaded into and executed by a machine, such as an EPROM, a gate array, aprogrammable logic device (PLD), a client computer, or a receivingmachine having the signal processing capabilities as described inexemplary embodiments above becomes an apparatus for practicing themethod described above and/or claimed herein. When implemented on ageneral-purpose processor, the program code combines with the processorto provide a unique apparatus that operates to invoke the functionalityof the methods and apparatus of described above and/or claimed herein.Further, any storage techniques used in connection with the methods andapparatus described above and/or claimed herein may invariably be acombination of hardware and software.

While preferred embodiments have been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope of the inventionis defined by the claims, and may include other examples of devices,methods, and articles of manufacture that occur to those skilled in theart. Such other examples are intended at least to be within the scope ofthe claims if they have structural elements that do not differ from theliteral language of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims and/or as allowed by law.

Furthermore, the skilled artisan will recognize the interchangeabilityof various features from different embodiments. Similarly, the variousfeatures described, as well as other known equivalents for each feature,can be mixed and matched by one of ordinary skill in this art.

What is claimed is:
 1. A portable articulated arm coordinate measurementmachine, comprising: a manually positionable articulated arm havingopposed first and second ends, the articulated arm including a pluralityof connected arm segments, the plurality of arm segments including afirst arm segment, each arm segment including at least one angularencoder for producing a signal corresponding to an angle of rotation; abase section connected to the second end; a probe connected to the firstend; a shaft fixedly attached to an inner portion of a first bearing andan inner portion of a second bearing, the shaft configured to rotateabout an axis passing substantially through a center of the firstbearing and a center of the second bearing, the shaft configured tofixedly couple with the first arm segment; a patterned disk fixedlyattached to the shaft, the patterned disk having a periodic pattern of ameasurable characteristic; a housing fixedly attached to an outerportion of the first bearing and an outer portion of the second bearing;a read head fixedly attached to the housing, the read head in proximityto the patterned disk, the read head configured to produce an electricalsignal in response to an angle of rotation about the axis of the shaftrelative to the housing, the patterned disk and the first arm segmentsupported for rotation about the axis by only the first bearing and thesecond bearing; and an electrical circuit configured to receive theelectrical signal, to provide an angle based at least in part on theelectrical signal, and to provide data corresponding to a position ofthe probe, the data based at least in part on the angle.
 2. The portablearticulated arm coordinate measurement machine of claim 1 wherein theaxis defines an axis of rotation for a swivel joint.
 3. The portablearticulated arm coordinate measurement machine of claim 1 wherein theaxis defines an axis of rotation for a hinge joint.
 4. The portablearticulated arm coordinate measurement machine of claim 1 wherein thepatterned disk is in optical communication with the read head.
 5. Theportable articulated arm coordinate measurement machine of claim 1wherein the patterned disk includes a feature having a characteristicmeasurable by the read head selected from the group consisting of:reflectivity characteristic, opacity characteristic, magnetic fieldcharacteristic, capacitance characteristic, inductance characteristicand surface roughness characteristic.
 6. A portable articulated armcoordinate measurement machine, comprising: a manually positionablearticulated arm having opposed first and second ends, the articulatedarm including a plurality of connected arm segments, the plurality ofarm segments including a first arm segment, each arm segment includingat least one angular encoder for producing a signal corresponding to anangle of rotation; a base section connected to the second end; a probeconnected to the first end; a shaft fixedly attached to an inner portionof a first bearing and an inner portion of a second bearing, the shaftconfigured to rotate about an axis passing substantially through acenter of the first bearing and a center of the second bearing, theshaft configured to fixedly couple with the first arm segment; a readhead fixedly attached to the shaft; a housing fixedly attached to anouter portion of the first bearing and an outer portion of the secondbearing; a patterned disk fixedly attached to the housing, the patterneddisk having a periodic pattern of a measurable characteristic, thepatterned disk arranged in proximity to the read head, the patterneddisk configured to produce an electrical signal in response to an angleof rotation about the axis of the shaft relative to the housing, theread head and the first arm segment supported for rotation about theaxis by only the first bearing and the second bearing; and an electricalcircuit configured to receive the electrical signal, to provide an anglebased at least in part on the electrical signal, and to provide datacorresponding to a position of the probe, the data based at least inpart on the angle.
 7. The portable articulated arm coordinatemeasurement machine of claim 6 wherein the axis defines an axis ofrotation for a swivel joint.
 8. The portable articulated arm coordinatemeasurement machine of claim 6 wherein the axis defines an axis ofrotation for a hinge joint.
 9. The portable articulated arm coordinatemeasurement machine of claim 6 wherein the patterned disk is in opticalcommunication with the read head.
 10. The portable articulated armcoordinate measurement machine of claim 6 wherein the patterned diskincludes a feature having a characteristic measurable by the read headselected from the group consisting of: reflectivity characteristic,opacity characteristic, magnetic field characteristic, capacitancecharacteristic, inductance characteristic and surface roughnesscharacteristic.